Is there any way to tell whether it is a blown head gasket or a cracked head without removing the head? Symptoms are white exhaust (steam) from a diesel engine and a loss of coolant. Some serious overheating occurred in the not too distant past

The odds of it being a cracked head are slim to zero. Before getting into any potential head gasket repair you really need to run a compression test on all cylinders. You do not want to go through the head gasket procedure only to end up with a shaky engine due to piston rings and/or valve issues.

You will need a special compression tester for the diesel engine. The tester used for gasoline engines will not work.